This invention relates to a thermoplastic resin composition and a molded article obtained therefrom and excellent in impact resistance, chemical resistance and resistance to thermal deformation.
Acrylonitrile-acrylic rubber-styrene terpolymers (AAS resins) are widely used due to having excellent properties in weather resistance, impact resistance, processability, etc., but insufficient in chemical resistance and heat resistance. On the other hand, thermoplastic aromatic polyester resins (hereinafter referred to as "polyester") are known as resins having excellent chemical resistance and heat resistance But these polyesters are poor in impact resistance, so that there has been proposed blend of the polyesters with ABS resins (acrylonitrile-polybutadiene rubber-styrene terpolymer resins), AAS resins, etc. (Japanese Patent Examined Publication No. 51-25261, Japanese Patent Unexamined Publication Nos. 54-150457, 57-94038, etc.). According to these proposals, since compatibility of ABS resins and AAS resins with polyesters is poor, there are obtained no composition having sufficiently satisfactorily balanced properties.
On the other hand, in order to improve weather resistance of ABS resins and surface quality of injection molded articles, Japanese Patent Examined Publication No. 47-47863 and U.S. Patent No. 4,393,172 disclose grafted polymers comprising a core formed by a crosslinked diene rubber, a first outer shell covering the core and formed by a crosslinked acrylic rubber, and a second outer shell formed thereon with a copolymer obtained by polymerizing glassy resin-forming monomer or monomers. These grafted polymers show good impact resistance but require further improvement. But these prior art references are quite silent on blending of these graft polymers with polyesters. Further, these prior art references are also quite silent on how to improve the impact resistance by other methods.
Japanese Patent Examined Publication No. 63-54729 (Japanese Patent Unexamined publication No. 58-187411) discloses the same grafted polymer as mentioned above, but obtained by stopping the polymerization in the course of formation of acrylic rubber. But this reference is quite silent on blending of such a grafted polymer with a polyester.
Further, U.S. Pat. No. 4,417,026 discloses a thermoplastic polyester composition for molding comprising 1 to 40% by weight of the grafted polymer disclosed U.S. Pat. No. 4,393,172 mentioned above, and 99 to 60% by weight of a saturated polyester. According to this reference, the impact strength of the saturated polyester can be improved by blending with the grafted polymer. But the present inventors found that such a blending was insufficient to obtain desirable impact resistance. Particularly, it was found that even if the grafted polymer may have excellent impact resistance, the blending of such a grafted polymer with polyesters remarkably lowered the impact resistance.